[LTO] Change std::sort to llvm::sort in response to r327219

[mgrang]

Summary

r327219 added wrappers to std::sort which randomly shuffle the container before sorting.
This will help in uncovering non-determinism caused due to undefined sorting
order of objects having the same key.

To make use of that infrastructure we need to invoke llvm::sort instead of std::sort.

Note: This patch is one of a series of patches to replace *all* std::sort to llvm::sort.
Refer D44363 for a list of all the required patches.

[mgrang]

Ping for reviews please.

[ruiu]

LGTM

llvm/trunk/lib/LTO/ThinLTOCodeGenerator.cpp

void ThinLTOCodeGenerator::run() {
   }
 
   // Compute the ordering we will process the inputs: the rough heuristic here
   // is to sort them per size so that the largest module get schedule as soon as
   // possible. This is purely a compile-time optimization.
   std::vector<int> ModulesOrdering;
   ModulesOrdering.resize(Modules.size());
   std::iota(ModulesOrdering.begin(), ModulesOrdering.end(), 0);
-  std::sort(ModulesOrdering.begin(), ModulesOrdering.end(),
+  llvm::sort(ModulesOrdering.begin(), ModulesOrdering.end(),
              [&](int LeftIndex, int RightIndex) {
                auto LSize = Modules[LeftIndex].getBuffer().size();
                auto RSize = Modules[RightIndex].getBuffer().size();
                return LSize > RSize;
              });
 
   // Parallel optimizer + codegen
   {
     ThreadPool Pool(ThreadCount);
     for (auto IndexCount : ModulesOrdering) {
       auto &ModuleBuffer = Modules[IndexCount];
       Pool.async([&](int count) {
         auto ModuleIdentifier = ModuleBuffer.getBufferIdentifier();